Methodology for Hydrogeological Risk Management of Drilled Steel Pipe Piles - A Case Study of Packhuskajen, Gothenburg

Sammanfattning

Drilled steel pipe piles is a piling method commonly used in areas where it is desirable to avoid e.g., displacement of masses, impacts on the surrounding environment, and large objects in the soil. However, drilled steel pipe piles are associated with the risk of groundwater leakage which could induce a chain of events leading to severe and costly economic, social, and environmental consequences. Hence, it is of interest for both the project owner and society to implement efficient and profitable risk-reducing measures to avoid possible consequences. Currently there is limited competence in the construction industry regarding how drilled steel pipe piles affects the mechanisms of the hydrogeological system. Therefore, this thesis proposes a methodology integrating a cost-effectiveness analysis (CEA) and the principles of the observational method to the ISO 31000:2018 framework. The methodology is applied to a case study, Packhuskajen, a quay renovation in central Gothenburg which faced leakages through drilled steel pipe piles during the first construction stage. A background study and interviews with employees working with Packhuskajen provided an understanding of the case study which acted as input for the CEA and the observational method. A probabilistic approach is used to manage the uncertain ground conditions when dealing with sub-surface constructions, where expert elicitation is used to quantify costs and uncertainties of risk-reducing measures for the CEA. There is a focus on economic, social, and environmental consequences to promote a sustainable risk management. Several relevant risk-reducing measures were identified for Packhuskajen, where the result shows that it is profitable to first observe potential groundwater impacts before implementing further measures. Further, the result shows that the proposed methodology can provide a decision support for managing hydrogeological risks associated with drilled steel pipe piles and due to its flexibility, it is also applicable for all types of projects where the ground conditions are uncertain. It also has the potential to reduce the risk of implementing measures when not needed, resulting in both cost- and resource savings. This thesis constitutes an important documentation of the knowledge gained at Packhuskajen enabling an increased understanding in the construction industry for future projects facing similar risks of how to manage hydrogeological risks associated with drilled steel pipe piles.